1. Field of the Invention
The present invention relates to a communication control method and a communication control system assigning a usable frequency band when conducting radio communication between a transmission side base station and a reception side base station in a radio communication network in which a plurality of radio stations are deployed.
2. Description of the Related Art
Conventionally, a usable frequency band is assigned to a radio link when conducting communication between a transmission side base station and a reception side base station on a radio communication network in which a plurality of radio stations are deployed. FIG. 1 shows a conventional assignment method of a frequency band,
In FIG. 1, radio stations 1 through 4 can be communicated with via radio links 12, 21, 13, 31, 34 and 43, For instance, if a new frequency band is assigned to a radio link 34 that is used from a transmission side radio station 3 to a reception side radio station 4, the frequency and reception power level transmitted by other radio stations are measured at an antenna of the reception side radio station 4, and the reception side radio station 4 then determines that frequencies whose reception power level is lower than a prescribed threshold are usable. As shown in FIG. 1(c), a frequency band that has no interference from other radio links is then assigned to the radio link 34 by selecting the frequency band from the frequencies that are determined as usable.
However, since interference that affects other radio links due to the assignment is not considered in the above conventional assignment method, interference that affects other radio links may occur due to the assignment of a frequency band to a radio link.
In other words, if a frequency band for the radio link 34 that is used from the transmission side radio station 3 to the reception side radio station 4 is assigned, as shown in FIG. 1(d), a frequency band that has no interference from the other radio links can be selected for the radio link 34 by measuring the frequency and reception power level received from the other radio stations at the antenna of the reception side radio station 4.
However, if the frequency band is assigned to the radio link 34 as shown in FIG. 1(c), great interference affecting the radio link 12 may occur in a case where the same frequency is simultaneously assigned to the radio link 34 and radio link 12 as shown in FIG. 1(b).
Therefore, not only interference from the other radio links but also interference that affects the other radio links should be considered in the assignment of a frequency band to a radio link. Otherwise, the reception power level of the interference may become greater at the other radio links and it may cause operational problems. However, recognition of the frequency bands and interference levels being used by all the radio links is difficult in the conventional assignment method.